The fundamental limits of the shared-link broadcast network with end-user-caches were studied in [1]}; this is a system where a server with \({\mathsf {N}}\)  files, of \({\mathsf {B}}\)  bits each, is connected to \({\mathsf {K}}\)  users through a shared error-free broadcast link and where each user has a cache of size \({\mathsf {M}}{\mathsf {B}}\)  bits.
A caching scheme includes two phases [1]}:
i) placement phase: each user stores \(\mathsf {MB}\)  bits in its cache without knowledge of later demands;
if each user directly copies some bits of the files, the placement is said to be uncoded;
ii) delivery phase: after each user has requested one file and according to cache contents, the server transmits \({\mathsf {R}}{\mathsf {B}}\)  bits in order to satisfy the user demands. The goal is to find \({\mathsf {R}}^{\star }\) , defined as the minimum rate such that any set of user demands (worst-case demands) can be satisfied.
In [1]}, Maddah-Ali and Niesen (MAN) proposed a caching scheme with uncoded cache placement and binary linear network coding for the delivery phase.
For \({\mathsf {N}}\ge {\mathsf {K}}\) , the MAN scheme in [1]} is optimal under the constraint of uncoded placement [5]} (the proof consists of connecting the caching problem to the index coding problem, and by cleverly leveraging a known outer bound for the caching problem).
A variation of the scheme in [1]} is optimal under the constraint of uncoded placement also for \({\mathsf {N}}< {\mathsf {K}}\)  [7]}.
Uncoded placement is known to be optimal to within a factor 2 [8]} for shared-link broadcast networks with end-user-caches.
